Variable volume constant pressure pump



Dec. 14, 1954 F. D. FUNsToN 2,696,788

VARIABLE VOLUME CONSTANT PRESSURE PUMP Filed Feb. 13, 1951 INVENTOR.

ATTORNEY United States Patent VARIABLE VOLUME CDNSTANT PRESSURE PUMP Frederick D. Funston, Tujunga, Calif., assigrior to Bendix Aviation Corporation, South Bend, Ind., .a corporation `of Delaware Application February 13, 1951, Serial No. 210,645

7 Claims. (Cl. 103-42) This invention relates to pumps for supplying liquid at constant pressure .and variable volume dependent upon the demand placed upon it. The invention `is particularly applicable to hydraulic power systems for vehicles such as tractors, airplanes, etc. in which the pump is coupled to the vehicle engine and runs constantly whether or not there is a `demand upon it.

An object of the invention is to provide a simple inexpensive and reliable pump of the type referred to.

Other more specific objects and features of the invention will appear from the description to follow.

Basically, a pump in accordance with 'the invention comprises ya plunger reciprocating in a cylinder, the cylinder having an inlet port in its side wall which is uncovered by the plunger at the end of its suction stroke, and having in its end an outlet port connected by a check valve with a delivery or pressure passage. To unload the pump when no fluid is being utilized, an exhaust port is provided in the wall of the cylinder in such position as to be covered by the plunger only near the end of its pumping stroke. This exhaust port is connected to a low pressure return line by .a valve that `is normally closed, but is opened by pressure in the delivery passage when that pressure rises to a predetermined value. When the delivery pressure is up, the plunger discharges iluid at low pressure through the exhaust port with little waste of power and heating of the fluid. Further in accordance with the invention, the exhaust port is so located that the plunger moves slightly past it on each stroke, whereby it pumps a small amount of fluid even when the exhaust valve is open, and a relief valve is provided to prevent the pressure in the delivery (pressure) passage from rising much above the predetermined pres sure at which the exhaust valve opens. The slight amount of fluid that is pumped when the pressure is up takes care f leakage losses and prevents the pressurerespon sive valve from constantly opening and closing during periods when there is no demand on the pump.

A full understanding of the invention may be had from the following detailed description with reference to the drawing in which:

Fig.` 1 is a schematic diagram of a single cylinder pump incorporating the invention;

Fig. 2 is; a schematic diagram of a triple cylinder pump incorporating the invention; and

Fig. 3 is a section taken on line Ill-III of Fig. 2.

Referring first to Fig. 1, the pump proper consists of a cylinder containing a plunger 11 which 1s repeatedly cycled through a full stroke by a constantly rotating cam 12. The piston is returned by a spring 13. In the bottom stroke position of the plunger 11, a' port 14 therein registers with an inlet port 15 in the cylinder to draw in fluid from a reservoir 16 through an intake pipe 35. During the upstroke of the plunger the iluid is discharged through one or both of two paths.

The main discharge path is through a discharge valve seat 17 in the top of the cylinder, past a spring-closed discharge valve 18, to a delivery port 19. When the pressure in the delivery port 19 is below a predetermined value, all of the fluid is displaced past the valve 18 and through the port 19.

A separate exhaust path for the escape of uid is provided through a port 20 in the cylinder wall near the upper end thereof, which port is covered by the upper end of the plunger 11 shortly before it reaches its upper limit position. This port 20 is connected by an exhaust passage 27 to a port 21 in a pressure-controlled exhaust ICC valve, which port is covered by a valve piston '22 whenever the pressure in the delivery port 19 is below a predetermined value. The valve piston 22 has an enlarged head 22a, the underside of which is connected by a passage 23 to the delivery port 19, so that the pressure of the delivered uid is constantly applied to the underside of the head 22a, in opposition to the force of a spring 24 that urges the valve piston 22 downward. It will be observed that as long as the delivery pressure is below a predetermined value, the valve piston 22 covers the port 21, and all of the luid displaced by upward movement of the pump plunger 11 is delivered to the delivery port 19. However when the pressure in the delivery port rises above the predetermined value, the lower end of the valve piston 22 uncovers the `port 21, and thereafter fluid within the cylinder 10 is exhausted through the port 2l) and the port 21 and through the intake pipe 35 back to the reservoir 16, during the major portion of the upward stroke of the piston 11. Very little work is performed by the plunger 11 during this portion of its stroke, because the fluid is returned to the reservoir at low pressure. During the small movement of the plunger 11 at the upper end of its stroke after it has covered the port 20, fluid is delivered past the valve 18 to the delivery port 19, and during this small portion of its stroke the plunger is doing work.

lf no uid is being withdrawn, the slight amount of uid supplied by the plunger 11 at the upper end of its stroke is vented past a conventional relief valve '25 through a passage 26 and through the port 15 back to the reservoir 16.

When the port 21 is closed by the valve 22, the plunger 11 draws a vacuum in the cylinder 10 during its down stroke until the intake port 15 is uncovered, whereupon the fluid rushes in. When the valve 22 is open, uid can enter the cylinder through Aport 20 while the plunger is moving through the major portion of its suction stroke.

It is old to run a pump continuously and vent all of the fluid through a relief valve back to the reservoir lwhen no fluid is being used. However, such systems are objectionable because they waste vpower and overheat the uid. The present invention pumps so little uid against high pressure, when no fluid is being drawn from `the port 19, that it can be readily vented through the relief valve 25 without an appreciable waste` of energy and without appreciable overheating. The bulk of the pumped fluid is returned to the reservoir at low pressure.

Fig. 2 shows the adaptation of the invention to a multi-cylinder pump. In this ligure three cylinders, A, B and C correspond in structure to the cylinder 10 of Fig. l, each having a similar piston, ports, etc. The only essential difference is in the construction of the pressure control valve. Thus, in Fig. 2, the exhaust passages 27a, 27b and 27C, each corresponding to the exhaust passages 27 of' Fig. l, connect to three different ports 21a,.21b and 21C associated with the pressure controlled exhaust piston valve 221, which corresponds to the exhaust valve 22 of Fig. l, except that it has three separate ports 30, 31 and 32 adapted to individually communicate the ports 21a, 2lb and 2`1c with an annular exhaust passage 33 in the piston valve which passage communicates with the reservoir through a port 41 in the body, and a passage 42 that connects to the return pipe 35.

A delivery passage 231 connects the delivery passages of all three cylinders A, B and C to each other, to a common delivery port 191, and to a port 43 in the Valve cylinder that communicates with a port 44 in the valve piston 221 in all positions of the latter.

The port 44 is connected by a passage 45 with a cylindrical counterbore 46 in the upper end of the valve piston, to develop pressure between the lower end of the counterbore and the lower end of a plug 47 which is slidably fitted in the counterbore. A cap 48 closes and seals the upper end of the valve cylinder and supports the plug 47 against upward movement.

The pressure uid in the counterbore opposes the spring 241, and when the delivery pressure rises to a predetermined value it moves the valve piston down to register the ports 30, 31 and 32 respectively with the p orts 21a, 2lb and 21C, and unload the pump by permitting fluid to leave the cylinder ports a, 20b and 20c at low pressure.

When the delivery pressure rises slightly above that at which the pump unloads, the valve piston 221 is further depressed to communicate the pressure port 43 with the return port 41 and relieve the pressure The piston valve 221 therefore performs both the function of unloading the pump and the function of relieving excess pressure, thereby eliminating the need of a sep arate relief valve as in Fig. 1. The arrangement of Fig. 2 has the advantage over that of Fig. l in that it is impossible for the relief valve to function before the unloading valve functions, and both can be adjusted to vary the delivery pressure by changing the loading of the single spring 241. A screw 50 is provided for this purpose.

Although for the purpose of explaining the invention a particular embodiment thereof has been shown and described, obvious modifications will occur to a person skilled in the art, and I do not desire to be limited to the exact details shown and described.

I claim:

1. A pump comprising: a cylinder having a plunger reciprocable therein and means for reciprocating said plunger; means defining a pressure iiuid delivery passage, and a check valve connecting one end of said cylinder to said delivery passage in response to pressure in said cylinder exceeding the pressure in said delivery passage; means defining an inlet passage adapted to be connected to a source of fluid to be pumped, and means for admitting uid from said inlet passage into said cylinder in response to suction in said cylinder; means defining an exhaust passage connected to said cylinder adjacent said one end thereof through a port in the side of the cylinder so longitudinally positioned as to be covered by said plunger prior to completion of its working Stroke for exhausting fluid therefrom at low pressure; exhaust valve means normally closing said exhaust passage; and means responsive to pressure in said delivery passage for'opening said exhaust valve in response to increase in the pressure in said delivery passage above a predetermined value.

2. A pump according to claim 1 having a relief valve connected to said delivery passage, said relief valve opening only in response to pressure higher than the pressure required to open said exhaust valve.

3. A pump comprising: a plurality of cylinders each having a plunger therein, and means for reciprocating said plungers through fixed strokes in out of phase relaj tion to each other; means defining a pressure iiuid delivery passage; individual check valves for said cylinders,

each connecting one end of its associated cylinder to said f delivery passage in response to pressure in said cylinder exceeding the pressure in said delivery passage; means defining an inlet passage adapted to be connected to a source of fluid to be pumped, and means for admitting fluid from said inlet passage into said cylinders in response to suction in said cylinders; means defining individual exhaust passages for said cylinders, each connected to its associated cylinder adjacent said one end thereof for exhausting fluid therefrom at low pressure; exhaust valve means normally closing all said exhaust passages; and means responsive to pressure in said delivery passage for opening said exhaust valve means in response to increase in the pressure in said outlet passage above a pre determined value.

4. A pump according to claim 3 in which said exhaust valve means comprises a pair of relatively slidable members in fluid sealing relation with each other, one of said members having a set of separate ports respectively connected to said individual exhaust passages, the other said member having a set of ports connected together and to exhaust, and movable simultaneously into and out or registration with said ports in said one member; spring means urging said members toward position in which said sets of ports are out of registration with each other; and means for applying the pressure in said delivery port be tween said two members in opposition to said spring means.

5. A pump according to claim3 in which said exhaust passage connects to said cylinder through a port in the side of the cylinder so longitudinally positioned as to be covered by said plunger prior to completion of the working stroke thereof.

6. A pump according to claim 5 having a relief valve connected to said delivery passage, said relief valve opening only in response to pressure higher than the pressure required to open said exhaust valve.

7. A pump comprising: a cylinder having a plunger reciprocable therein and means for reciprocating said plunger; means defining a pressure fluid delivery passage, and a check valve connecting one end of said cylinder to said delivery passage in response to pressure in said cylinder exceeding the pressure in said delivery passage; means defining an inlet passage adapted to be connected to a source of fluid to be pumped, and means for admitting fluid from said inlet passage into said cylinder in response to suction in said cylinder; means defining an exhaust passage connected to said cylinder adjacent said one end thereof for exhausting fluid therefrom at low pressure; exhaust valve means normally closing said exhaust passage; and means responsive to pressure in said delivery passage for opening said exhaust valve in response to increase in the pressure in said delivery passage above a predetermined value; said exhaust valve means comprising a pair of relatively sliding members in iiuid sealing relation, said members having a first pair of cooperating ports connected in said exhaust passage for closing said passage in one relative position of said members and opening said passage in response to predetermined relative movement from said one position; said members having a second pair of cooperating ports, one connected to said delivery passage and the other connected to a relief passage; spring means urging said members toward said one relative position; and means for applying the pressure in said delivery port between said two members in opposition to said spring means; the ports of said second pair being so positioned in their rcspective valve members that they are out of registration in said one relative position of said members and move into registration in response to relative movement of said members away from said one position in excess of said predetermined movement.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,451,481 Vincent Apr. 10, 1923 1,801,414 Davis Apr. 2l, 1931 2,313,351 Magnuson Mar. 9, 1943 2,510,150 Stephens June 6, 1950 

